A compound having a mesogenic group is used for various optical materials. For example, a polymer having uniform alignment can be prepared by subjecting a polymerizable composition containing a compound having a mesogenic group being in a liquid crystal state to alignment, and then performing polymerization. Such a polymer can be used for a polarizing plate, a phase difference plate, and the like which are necessary for a display. In many cases, in order to satisfy required optical properties, polymerization rate, solubility, melting point, glass transition temperature, polymer transparency, mechanical strength, surface hardness, heat resistance, and light resistance, a polymerizable composition containing two or more polymerizable compounds is used. At that time, it is required for the compound having a mesogenic group to be used to provide favorable physical properties to the polymerizable composition without adversely affecting other properties.
In regard to the optically anisotropic body, it is desirable that the optically anisotropic body (film) used for a display device, an optical element, or the like is less likely to discolor in the case of being used for a long period of time, from the viewpoint of reliability. As a cause of discoloration, for example, exposure to ultraviolet and visible light from various light sources such as backlight, indoor light, and sunlight, and to various heat sources causes deterioration of the optically anisotropic body. In addition, in the case where the polymer is insufficient, discoloration may occur even by heating, ultraviolet irradiation, or the like performed to complete polymerization (PTLs 1 and 2). In the case where an optically anisotropic body which discolors or an optically anisotropic body which is likely to discolor is used, for example, for a purpose of expending a viewing angle and converting polarization of a liquid crystal display or the like, there is a problem that the quality of a display product is greatly deteriorated, since brightness or contrast of the display deteriorates, or hue of the image changes along with the use time of the display.
On the other hand, in order to improve a viewing angle of a liquid crystal display, it is required to reduce wavelength dispersibility of birefringence of a phase difference film or to reverse the wavelength dispersibility. As a material for the above purpose, various polymerizable liquid crystal compounds having reverse wavelength dispersibility or low wavelength dispersibility have been developed. However, a polymerizable liquid crystal compound having reverse wavelength dispersibility or low wavelength dispersibility has low solubility in solvents used generally, and in the case where the polymerizable composition is applied on a substrate and then polymerized, there has been a problem that unevenness easily occurred (PTL 3).
Therefore, there has been a demand for a polymerizable composition which has favorable solubility, is less likely to discolor, and has reverse wavelength dispersibility or low wavelength dispersibility.